Field of the Invention
The present invention relates to an image sensor and an image capturing apparatus that uses the same.
Description of the Related Art
In recent years, image sensors such as CCD image sensors and CMOS image sensors have become widely used in single-lens reflex digital cameras and video cameras. Usually, an image sensor has a flat silicon substrate on which photodiodes (PD) or the like that perform photoelectric conversion are formed. Light that has passed through an imaging lens is received by the image sensor, and whereas light is perpendicularly incident on the image sensing plane of the image sensor in the central region of the image sensing plane, light is obliquely incident on the peripheral region of the image sensing plane. This results in the generation of a difference between the amounts of light that is incident on the pixels and shifting of the focal position due to lens aberration.
To address this, Japanese Patent Laid-Open No. 2014-116380 discloses a technique in which optical characteristics are enhanced by changing the configuration of the image sensor. Specifically, by curving the image sensor into a concave surface, a light shading correcting effect can be obtained and irregularity in the amount of light on the light receiving surface can be reduced. Also, a curvature of field correcting effect can also be obtained with a concave surface.
Incidentally, if tensile stress is applied when the image sensor is curved, the silicon energy band gap widens and dark current decreases. Due to this characteristic, a problem arises in that the amount of dark current in the image sensing plane is different between the region subjected to tensile stress and the region that is not subjected to tensile stress when the image sensor is curved. Also, even if the entire image sensing plane is subjected to tensile stress, the magnitude of the tensile stress changes depending on the region, and a difference in the amount of dark current similarly occurs in the image sensing plane. A difference in the amount of dark current in the image sensing plane is a cause of image quality deterioration when performing long-exposure image capture or capturing an image in a high-temperature environment, for example.